Without knowing where you live, how deep the gravel is and which plants, I would say the gravel could slow down the spread of the plants. If you live in a hot climate and it's a sunny spot, the gravel could heat up enough to effect the plants as well. Aztec grass aka Liriope will most likely do just fine as it's very hardy.

I live in the panhandle of Florida. The gravel is about 2in thick. I have the aztec grass, fountain grass, and a plant that I don't have the name for (dark purple/red, similar to aztec grass in shape but fewer strands and much longer, any idea?)

Kjac, you are very welcome! Your grasses should do just fine. Considering your location and description, I'm thinking your other plant might be a variety of New Zealand flax aka Phormium. Any of these look like it?http://images.google.com/images?hl=e...-8&sa=N&tab=wi